One conventional system and method for manufacturing concrete modular housing units relies on form assemblies that are detachably connected to a concrete floor slab. Concrete is poured or pumped into the wall space between the wall forms and onto roof forms where the concrete is spread and leveled. After the concrete has taken a substantial set and begun to harden, the forms are removed and hauled to the next concrete floor slab. Typically, the two form assemblies remain connected together at the location where the housing units will be erected. See, e.g., U.S. Pat. No. 4,246,060, incorporated by reference herein.
Another conventional system and method for manufacturing concrete modular housing units uses a molding apparatus for molding in place walls of a structure poured on a concrete floor. The apparatus has a central support member to which are moveably attached wall molds and corner molds cooperate with exterior molds to form a cast structure. Concrete is pumped into the cast structure, and, after the concrete hardens, the exterior molds are removed and then transported to another site. See, e.g., U.S. Pat. No. 4,650,150, incorporated by reference herein.
Yet another system and method for manufacturing concrete modular housing units comprises a modular floor deck which is affixed to a plant floor. Tracks are leveled and secured to the plant floor. Interior cores are then placed on the form deck and secured to the deck. Side wall forms are then placed on the tracks and leveled and permanently secured to the tracks. A removable chase core is then positioned in the space between the inside cores to form a utility chase. Once all the form components are properly aligned, the casting process begins. Typically, this may include spraying oil on the walls to ensure the concrete will not stick to the forms. Then a wire cage may be placed between the forms followed by the placement of a wire mesh cage. The necessary conduits and electrical boxes are then secured. Next, the outer wall forms are closed and secured together by bolting them to the base as well as other walls. Concrete is then poured in the form and the top may be finished using bull floats and trowels to achieve a smooth and level finish roof. The module then cures for several hours until the concrete has achieved the necessary strength. Once the strength is achieved the chase core is removed and the walls are then unbolted in the tracks. The module is then lifted using a mobile crane. The entire process typically takes about 24 hours.
However, using the conventional systems and methods described above, the forms are not useable until the concrete has hardened and the completed housing unit is removed therefrom. This prevents the same forms from being used more than once a day. Such a design significantly slows the manufacturing process of concrete modular housing units.
The exterior walls of concrete modular housing units typically have a smooth flat finish. Often, the exterior surface is removed (e.g., by sand blaster or with a high pressure water jet) to expose the aggregate (rock) in the concrete and create exposed aggregate walls. However, vertically pouring concrete into the wall forms causes the heavier aggregate to settle at the bottom of the wall. A vibrator is often used in the manufacturing process which further induces faster settling of the aggregate. Additionally, the excessive weight and gravitational forces of the concrete to be poured located above a ten or twelve foot form results in loss of control of the placement of the aggregate in the finished wall. The result of the aforementioned problems is typically an exterior wall having a non-uniform distribution of the aggregate and thus an uneven finish.